1. Field of the Invention
The present invention relates to a fingerprint image processing device and fingerprint image processing method applicable for instance in a fingerprint check device.
2. Description of Related Art
In a fingerprint check device of the conventional art, a fingerprint image was captured from the placing of the fingertip at the specified placement position and for instance the entry or exit from a room was allowed by a check of that fingerprint image.
In this kind of fingerprint check device, a technique was proposed in which placement of a finger was detected and processing started by monitoring changes in the sequentially input image data. This kind of device permitted use of a simple overall structure since there was no need to provide a separate device to detect placement of fingers.
However, when commencing image processing based merely on changes in image data, processing also commenced just by placing an object other than the finger at the placement position of the fingerprint check device. Another problem was that in brightly lit environments, processing was started just by a shadow passing over the finger placement position. Due to these reasons, the conventional art had the problem that reliable capturing of fingerprint images was difficult when processing started merely based on changes in image data.
In view of the above problems with the conventional art it is therefore an object of this invention to provide a fingerprint image processing device and fingerprint image processing method capable of starting processing of the fingerprint image only when the finger is correctly placed and the fingerprint image can be reliably captured.
In order to resolve the above mentioned problems, this invention detects the degree of the ripple showing changes in the spatial brightness level of the fingerprint image, and perform reliable image processing by starting the processing of the fingerprint image based on the degree of ripple.
In other words, this invention detects the degree of ripple indicating the spatial brightness level changes of the fingerprint image from the fingerprint image input by the image input technique for capturing the image of the fingerprint and then starts processing of the fingerprint image when the results of ripple detection exceed a specified threshold value.
When the finger is placed on the finger placement position, a fingerprint image is acquired having a brightness level corresponding to the pattern of the fingerprints. The brightness level of the fingerprint image is a pattern alternately changing between a high brightness portion and a low brightness portion within a short period. The change in the spatial brightness level is referred to a ripple in these specifications. Accordingly, the fingerprint image has a ripple when the finger is placed in the finger placement position. However, when an object other than a finger but having the same image projection area of the finger is placed on the finger placement position or when a shadow falls across the finger placement position in brightly lit environments, a change in the brightness level is then generated equivalent to that level when a finger is placed on the finger placement position, however this image will not contain the ripple of the brightness level characterized by a fingerprint image. Consequently, to acquire and process an actual fingerprint image, a ripple is detected at a degree showing a change in the spatial brightness level of the image acquired as the fingerprint image, when the detection data from this ripple exceeds a specified threshold value, the processing of the fingerprint image starts in order to allow reliably acquiring the fingerprint image when the finger is actually placed in the specified finger placement position.